function goTop(){ 

var _btn = document.getElementById("goTop"); 

if (document.documentElement && document.documentElement.scrollTop) { 

var _con = document.documentElement; 

} else if (document.body) { 

var _con = document.body; 

} 

window.onscroll = set; 

_btn.style.left = document.documentElement.scrollWidth/2 + 500 + "px"; 

_btn.onclick = function (){ 

_btn.style.display = "none"; 

window.onscroll = null; 

this.timer = setInterval(function() { 

_con.scrollTop -= Math.ceil(_con.scrollTop * 0.2); 

if (_con.scrollTop == 0) clearInterval(_btn.timer, window.onscroll = set); 

},10); 

}; 

function set() { 

_btn.style.display = _con.scrollTop ? 'block': "none"; 

} 

}; 

document.write("<div id=\"goTop\" style=\"font-size:12px; width:20px; height:55px; background:#d18d55; color:#fff; line-height:14px; position:fixed; bottom:30px; display:none; cursor:pointer; text-align:center; padding:5px 0; z-index:1; _position:absolute; _top:expression(eval(patMode && patMode == \'CSS1Compat\') ? documentElement.scrollTop + (documentElement.clientHeight - this.clientHeight) - 30 : document.body.scrollTop + (document.body.clientHeight - this.clientHeight) - 30);\">返<br />回<br />顶<br />部</div>"); 

window.onscroll = goTop; // JavaScript Document 
